Showing papers on "Silicon carbide published in 2004"

Silicon carbide : recent major advances

Abstract: Zero- and Two-Dimensional Native Defects.- Defect Migration and Annealing Mechanisms.- Hydrogen in SiC.- Electronic Properties of Stacking Faults and Thin Cubic Inclusions in SiC Polytypes.- Principles and Limitations of Numerical Simulation of SiC Boule Growth by Sublimation.- Defect Formation and Reduction during Bulk SiC Growth.- High Nitrogen Doping During Bulk Growth of SiC.- Homoepitaxial and Heteroepitaxial Growth on Step-Free SiC Mesas.- Low-Defect 3D-SiC Grown on Undulant-Si (001) Substrates.- New Development in Hot Wall Vapor Phase Epitaxial Growth of Silicon Carbide.- Formation of SiC Thin Films by Ion Beam Synthesis.- Atomic Structure of SiC Surfaces.- The Continuum of Interface-Induced Gap States.- Contributions to the Density of Interface States in SiC MOS Structures.- Properties of Nitrided Oxides on SiC.- Hall Effect Studies of Electron Mobility and Trapping at the SiC/SiO2 Interface.- Optical Properties of SiC.- Cyclotron Resonance Studies of Effective Masses and Band Structure in SiC.- Electronic Structure of Deep Defects in SiC.- Phosphorus-Related Centers in SiC.- Hall Scattering Factor for Electrons and Holes in SiC.- Radiotracer Deep Level Transient Spectroscopy.- Vacancy Defects Detected by Positron Annihilation.- Characterization of Defects in SiC Crystals by Raman Scattering.- Characterization of Low-Dimensional Structures in SiC Using Advanced Transmission Electron Microscopy.- Synchrotron White Beam X-ray Topography and High Resolution X-ray Diffraction Studies.- Ohmic Contacts for Power Devices on SiC.- Micromachining of SiC.- Surface Preparation Techniques for SiC Wafers.- Epitaxial Growth and Device Processing of SiC on Non-Basal Planes.- SiC Power Bipolar Transistors and Thyristors.- High-Voltage SiC Devices.- Power MOSFETs in 4H-SiC.- Normally-Off Accumulation-Mode Epi-Channel Field Effect Transistor.- Development of SiC Devices for Microwave and RF Power Amplifiers.- Advances in SiC Field Effect Gas Sensors

Ultrahigh-quality silicon carbide single crystals

Abstract: Silicon carbide (SiC) has a range of useful physical, mechanical and electronic properties that make it a promising material for next-generation electronic devices. Careful consideration of the thermal conditions in which SiC [0001] is grown has resulted in improvements in crystal diameter and quality: the quantity of macroscopic defects such as hollow core dislocations (micropipes), inclusions, small-angle boundaries and long-range lattice warp has been reduced. But some macroscopic defects (about 1-10 cm(-2)) and a large density of elementary dislocations (approximately 10(4) cm(-2)), such as edge, basal plane and screw dislocations, remain within the crystal, and have so far prevented the realization of high-efficiency, reliable electronic devices in SiC (refs 12-16). Here we report a method, inspired by the dislocation structure of SiC grown perpendicular to the c-axis (a-face growth), to reduce the number of dislocations in SiC single crystals by two to three orders of magnitude, rendering them virtually dislocation-free. These substrates will promote the development of high-power SiC devices and reduce energy losses of the resulting electrical systems.

Processing, properties and arc jet oxidation of hafnium diboride/silicon carbide ultra high temperature ceramics

Abstract: The processing and properties of HfB2-20 vol%SiC ultra high temperature ceramics were examined. Dense billets were fabricated by hot-pressing raw powders in a graphite element furnace for 1 h at 2200°C. Specimens were then tested for hardness, mechanical strength, thermal properties and oxidation resistance in a simulated re-entry environment. Thermal conductivity of the current materials was found to be less than previous work had determined while the strength was greater. Oxidation testing of two flat-face models was conducted, at two conditions, for two 10-min durations each. It was concluded that passive oxidation of SiC plays a role in determining the steady-state surface temperatures below 1700°C. Above 1700°C, temperatures are controlled by the properties of a thick HfO2 layer and active oxidation of the SiC phase.

Reactive Hot Pressing of ZrB2–SiC Composites

Abstract: A ZrB 2 -SiC composite was prepared from a mixture of zirconium, silicon, and B 4 C via reactive hot pressing. The three-point bending strength was 506 ± 43 MPa, and the fracture toughness was 4.0 MPa.m 1/2 . The microstructure of the composite was observed via scanning electron microscopy; the in-situ-formed ZrB 2 and SiC were found in agglomerates with a size that was in the particle-size ranges of the zirconium and silicon starting powders, respectively. A model of the microstructure formation mechanism of the composite was proposed, to explain the features of the phase distributions. It is considered that, in the reactive hot-pressing process, the B and C atoms in B 4 C will diffuse into the Zr and Si sites and form ZrB 2 and SiC in situ, respectively. Because the diffusion of Zr and Si atoms is slow, the microstructure (phase distributions) of the obtained composite shows the features of the zirconium and silicon starting powders.

Modified Deal Grove model for the thermal oxidation of silicon carbide

Abstract: A modified Deal Grove model for the oxidation of 4H-SiC is presented, which includes the removal of the carbon species. The model is applied to data on the oxidation rates for the (0001) Si, (0001) C, and (1120) a faces, which are performed in 1 atm dry oxygen and in the temperature range 950–1150 °C. Analysis within the model provides a physical explanation for the large crystal-face dependent oxidation rates observed.

Optical and electrical transport properties in silicon carbide nanowires

Abstract: We report on the optical and electrical transport properties of single-crystalline silicon carbide nanowires (SiC NWs). The NWs were fabricated by a chemical vapor deposition process, and had diameters of <100nm and lengths of several μm. X-ray diffraction and transmission electron microscopy analysis showed the single-crystalline nature of NWs with a growth direction of ⟨111⟩. Photoluminescence characterization showed blue emission at room temperature. The electrical measurements from a field effect transistor structure on individual NWs showed n-type semiconductor characteristics. The resistivity and estimated electron mobility on the NWs are 2.2×10−2Ωcm for 0V of gate voltage and 15cm2∕(Vs), respectively. Our low-resistivity SiC NWs could be applied to a high-temperature operation sensor and actuator due to its own excellent electrical and optical properties.

Method of depositing dielectric films

Abstract: A method of forming a silicon carbide layer for use in integrated circuit fabrication processes is provided. The silicon carbide layer is formed by reacting a gas mixture comprising a silicon source, a carbon source, and a dopant in the presence of an electric field. The as-deposited silicon carbide layer has a compressibility that varies as a function of the amount of dopant present in the gas mixture during later formation.

Materials science: Silicon carbide in contention

Abstract: Silicon carbide is a highly desirable material for high-power electronic devices — more desirable even than silicon. And now the problem of producing large, pure wafers of the carbide could be solved.

Methods for the reduction and elimination of particulate contamination with cvd of amorphous carbon

Abstract: A method is provided for forming an amorphous carbon layer, deposited on a dielectric material such as oxide, nitride, silicon carbide, carbon doped oxide, etc., or a metal layer such as tungsten, aluminum or poly-silicon. The method includes the use of chamber seasoning, variable thickness of seasoning film, wider spacing, variable process gas flows, post-deposition purge with inert gas, and post-deposition plasma purge, among others, to make the deposition of an amorphous carbon film at low deposition temperatures possible without any defects or particle contamination.

Comparison of Wide-Bandgap Semiconductors for Power Electronics Applications

Abstract: Recent developmental advances have allowed silicon (Si) semiconductor technology to approach the theoretical limits of the Si material; however, power device requirements for many applications are at a point that the present Si-based power devices cannot handle. The requirements include higher blocking voltages, switching frequencies, efficiency, and reliability. To overcome these limitations, new semiconductor materials for power device applications are needed. For high power requirements, wide-bandgap semiconductors like silicon carbide (SiC), gallium nitride (GaN), and diamond, with their superior electrical properties, are likely candidates to replace Si in the near future. This report compares wide-bandgap semiconductors with respect to their promise and applicability for power applications and predicts the future of power device semiconductor materials.

Technological Breakthroughs in Growth Control of Silicon Carbide for High Power Electronic Devices

Abstract: Technological breakthroughs in growth control of SiC are reviewed. Step-controlled epitaxy by using off-axis SiC {0001} substrates to grow high-quality epitaxial layer is explained in detail. The introduction of substrate off-angles brings step-flow growth, which easily makes polytype replication of SiC at rather low temperatures. Off-angle dependence, rate-determining processes, and temperature dependence of growth rate are discussed. Prediction, whether step-flow growth or two-dimensional nucleation does occur, is given as a function of off-angle, growth temperature, and growth rate. Optical and electrical properties of undoped epitaxial layers are characterized. Impurity doping during the growth is explained. Recent progresses in peripheral technologies for realization of power electronic devices, such as bulk growth, epitaxial growth, ion implantation, MOS interface, ohmic contacts, are introduced. Finally application to high-power electronic devices is briefly described.

Yttrium Silicate Coatings for Oxidation Protection of Carbon–Silicon Carbide Composites

Abstract: Yttrium silicate (Y 2 SiO 5 ) coatings complement SiC coatings for protecting ceramic multilayer composite materials based on carbon-fiber-reinforced SiC composites (C-SiC). Thick (100 μm), dense Y 2 SiO 5 coatings were prepared by dip coating, using concentrated aqueous slips. The resulting phases were studied by taking into account the simultaneous presence of oxide and non-oxide materials, which affected the chemical stability of the coatings. Thick, mechanically stable coatings were obtained by sintering in carbon crucibles and a SiC bed in an argon-flow furnace. Pure Y 2 SiO 5 coatings completely separated from the SiC substrates. A high percentage of Y 2 Si 2 O 7 was necessary to fit the thermal expansion coefficients and ensure the stability of the coatings. Oxidation resistance of the coated substrates was investigated by isothermal and stepwise oxidation tests.

Band alignment and defect states at SiC/oxide interfaces

Abstract: Comparative analysis of the electronic structure of thermally oxidized surfaces of silicon and silicon carbide indicates that in both cases the fundamental (bulk-band-related) spectrum of electron states is established within less than 1 nm distance from the interface plane. The latter suggests an abrupt transition from semiconductor to insulator. However, a large density of interface traps is observed in the oxidized SiC, which are mostly related to the clustering of elemental carbon during oxide growth and to the presence of defects in the near-interfacial oxides. Recent advancements in reducing the adverse effect of these traps suggest that the SiC oxidation technology has not reached its limits yet and fabrication of functional SiC/oxide interfaces is possible.

Ceramic substrate for a light emitting diode where the substrate incorporates ESD protection

Abstract: A metal oxide varistor comprising one or more zinc oxide layers is formed integral to a ceramic substrate to provide ESD protection of a semiconductor device mounted to the substrate. The portion of the ceramic substrate not forming the varistor may be aluminum oxide, aluminum nitride, silicon carbide, or boron nitride. The varistor portion may form any part of the ceramic substrate, including all of the ceramic substrate.

Impact ionization coefficients of 4H silicon carbide

Abstract: Anisotropy of the impact ionization coefficients of 4H silicon carbide is investigated by means of the avalanche breakdown behavior of p+n diodes on (0001) and (112¯0) 4H silicon carbide epitaxial wafers. The impact ionization coefficients are extracted from the avalanche breakdown voltages and the multiplication of a reverse leakage current, due to impact ionization of these p+n diodes. The breakdown voltage of a p+n diode on a (112¯0) wafer is 60% of that on a (0001) wafer, and the extracted impact ionization coefficients of 4H silicon carbide show large anisotropy. We have shown that the anisotropy of the impact ionization coefficients is related to the anisotropy of carrier heating and drift velocity, which are due to the highly anisotropic electronic structure of 4H silicon carbide.

High‐Strength Porous Silicon Carbide Ceramics by an Oxidation‐Bonding Technique

Abstract: Porous silicon carbide (SiC) ceramics were fabricated by an oxidation-bonding process in which the powder compacts are heated in air so that SiC particles are bonded to each other by oxidation-derived SiO2 glass. Because of the crystallization of amorphous SiO2 glass into cristobalite during sintering, the fracture strength of oxidation-bonded SiC ceramics can be retained to a relatively high level at elevated temperatures. It has been shown that the mechanical strength is strongly affected by particle size. When 0.6 μm SiC powders were used, a high strength of 185 MPa was achieved at a porosity of ∼31%. Moreover, oxidation-bonded SiC ceramics were observed to exhibit an excellent oxidation resistance.

Role of Carbon in the Sintering of Boron‐Doped Silicon Carbide

Abstract: The effect of carbon on the sintering of boron-doped SiC was studied. The free carbon present in the green compact was found to react with the SiO2 covering the surfaces of the SiC particles; however, even if no carbon was added, the surface SiO2 reacted with the SiC itself at a slightly higher temperature. This latter reaction was associated with the onset of substantial pore growth in the shrinking green body, which, as the pores continued to grow at higher temperatures, prevented complete densification. Therefore, the reaction of the SiC with the SiO2 may have led to the fracture of interparticle contacts, resulting in the onset of coarsening. Thus, the role of the carbon was to prevent reaction between the SiC and the surface SiO2, by removing the SiO2 at a temperature below that at which this reaction could occur.

Sintered ceramic compact and ceramic filter

Abstract: A sintered ceramic compact, characterized in that it comprises ceramic coarse particles and a polycrystalline binding layer composed of ceramic fine particles and/or aggregates thereof which are present among the ceramic coarse particles in such a manner as to link them and have an average particle diameter less than that of said coarse particles; and a ceramic filter manufactured by using the sintered ceramic compact. The sintered ceramic compact or the ceramic filter can suppress the occurrence of a large crack due to the break of particles of silicon carbide in the case wherein a thermal stress is applied to the sintering compact in a re-treatment or the like, can suppress the deterioration of a catalyst carried on it in the case that it is re-treated repeatedly, and thus can be used stably for a long period of time.

High Surface Area Silicon Carbide Whiskers and Nanotubes Nanocast Using Mesoporous Silica

Abstract: We report here the formation of high surface area silicon carbide materials comprising whiskers and nanotubes via a synthesis route, which utilizes mesoporous silica as sacrificial solid template. The silicon carbide materials are obtained via carbothermal reduction of mesoporous silica/carbon (i.e., SBA-15/sucrose) composites. Varying the carbothermal reduction conditions (i.e., temperature or duration) readily modifies the morphology of the silicon carbide so as to obtain whiskers or nanotubes. The whiskers, which grow in the [111] direction, are achieved by subjecting the mesoporous silica/carbon composites to carbothermal reduction at high temperature (1250 or 1300 °C) for reduction periods of up to 14 h. For reduction periods of up to 14 h, using the higher temperature (1300 °C) optimizes whisker formation. The diameter of the whiskers is 50−90 nm and their length is typically greater than 20 μm. The surface area of the whisker containing SiC materials varies between 120 and 145 m2/g, while their por...

Fixed Abrasive Diamond Wire Saw Slicing of Single-Crystal Silicon Carbide Wafers

Abstract: This article investigates the slicing of single-crystal silicon carbide (SiC) with a fixed abrasive diamond wire. A spool-to-spool rocking motion diamond wire saw machine using a 0.22 mm nominal diameter diamond wire with 20 µm average size diamond grit was used. The effect of wire downfeed speed on wafer surface roughness and subsurface damage was first investigated. The surface marks generated by loose diamond grit and stagnation of the wire during the change of the wire-cutting direction were studied. The use of scanning acoustic microscopy (SAcM) as a nondestructive evaluation method to identify the subsurface damage was explored. Effects of using a new diamond wire on cutting forces and surface roughness were also investigated. Scanning electron microscopy has been used to examine the machined surfaces and wire wear. This study demonstrated the feasibility of fixed abrasive diamond wire cutting of SiC wafers and the usage of a SAcM to examine the subsurface damage.

Epitaxial growth of group III nitrides on silicon substrates via a reflective lattice-matched zirconium diboride buffer layer

Abstract: A semiconductor structure and fabrication method is provided for integrating wide bandgap nitrides with silicon. The structure includes a substrate, a single crystal buffer layer formed by epitaxy over the substrate and a group III nitride film formed by epitaxy over the buffer layer. The buffer layer is reflective and conductive. The buffer layer may comprise B an element selected from the group consisting of Zr, Hf, Al. For example, the buffer layer may comprise ZrB 2 , AlB 2 or HfB 2 . The buffer layer provides a lattice match with the group m nitride layer. The substrate can comprise silicon, silicon carbide (SiC), gallium arsenide (GaAs), sapphire or Al 2 O 3 . The group m nitride material includes GaN, AIN, InN, AlGaN, InGaN or AlInGaN and can form an active region. In a presently preferred embodiment, the buffer layer is ZrB 2 and the substrate is Si(111) or Si(100) and the group III nitride layer comprises GaN. The ZrB 2 buffer layer provides a reflective and conductive buffer layer that has a small lattice mismatch with GaN. The semiconductor structure can be used to fabricate active microelectronic devices, such as transistors including field effect transistors and bipolar transistors. The semiconductor structure also can be used to fabricate optoelectronic devices, such as laser diodes and light emitting diodes

Three-dimensional crystalline SiC nanowire flowers

Abstract: Several techniques have already been developed for synthesizing silicon carbide (SiC) material in the form of nanospheres and nanowires/rods. Here, we report the synthesis of a distinctly different kind of SiC nanostructure in the form of three-dimensional crystalline nanowire-based flower-like structures. Interest in such structures centres around the combination of a simple growth process based on SiC nanowire formation, with a resultant structure having potentially complex mechanical and optical properties, the latter a consequence of the wide band gap of bulk SiC. The synthesis of these SiC nanowire flowers is via a vapour–liquid–solid (VLS) process, on which a detailed study of both the chemical and structural composition has been carried out.

Reliability of SiC MOS devices

Abstract: Fundamental limitations to oxide reliability are analyzed in silicon carbide based devices. A barrier height primarily determined by band offsets between metal/SiC and the dielectric, and the electric field in the dielectric results in tunneling current into the dielectric, resulting in its degradation. Since band offsets for SiC to most dielectrics are smaller than those with respect to Si, a lower reliability is expected for SiC-dielectric based devices as compared to Si MOS devices. Other researchers have correlated interface states in the SiC–oxide as tunneling sites that increase gate leakage currents and influence the barrier to tunneling. Depending on the allowed maximum electric field in the gate oxide, there exists a trade-off between on-state resistance and SiC MOS reliability.

Passivation of hexagonal SiC surfaces by hydrogen termination

Abstract: Surface hydrogenation is a well established technique in silicon technology. It is easily accomplished by wet-chemical procedures and results in clean and unreconstructed surfaces, which are extremely low in charged surface states and stable against oxidation in air, thus constituting an ideal surface preparation. As a consequence, methods for hydrogenation have been sought for preparing silicon carbide (SiC) surfaces with similar well defined properties. It was soon recognized, however, that due to different surface chemistry new ground had to be broken in order to find a method leading to the desired monatomic hydrogen saturation. In this paper the results of H passivation of SiC surfaces by high-temperature hydrogen annealing will be discussed, thereby placing emphasis on chemical, structural and electronic properties of the resulting surfaces. In addition to their unique properties, hydrogenated hexagonal SiC {0001} surfaces offer the interesting possibility of gaining insight into the formation of silicon- and carbon-rich reconstructions as well. This is due to the fact that to date hydrogenation is the only method providing oxygen-free surfaces with a C to Si ratio of 1:1. Last but not least, the electronic properties of hydrogen-free SiC {0001} surfaces will be alluded to. SiC {0001} surfaces are the only known semiconductor surfaces that can be prepared in their unreconstructed (1 × 1) state with one dangling bond per unit cell by photon induced hydrogen desorption. These surfaces give indications of a Mott–Hubbard surface band structure.

Thermal conductivity of silicon carbide densified with rare-earth oxide additives

Abstract: In order to fabricate SiC ceramics of high thermal conductivity, a submicrometer-size β–SiC powder doped with various amounts of combinations of Y 2 O 3 and La 2 O 3 as sintering additives was hot-pressed at 2000 °C under 40 MPa for 2 h in Ar, and some hot-pressed specimens were subsequently annealed at 1900 °C for 4 h in Ar. The phase compositions and microstructures of the hot-pressed and the annealed SiC ceramics were characterized, and their thermal conductivities were measured by a laser-flash technique. By adding 1 mol% or more additives, full densification was achieved and the materials had thermal conductivities in excess of 166 W/(m K). The thermal conductivities further improved to over 200 W/(m K) after annealing. An explanation on the correlation between thermal conductivity, phase composition, and microstructure was proposed.

Electro-chemical mechanical polishing of silicon carbide

Abstract: In an effort to improve the silicon carbide (SiC) substrate surface, a new electro-chemical mechanical polishing (ECMP) technique was developed. This work focused on the Si-terminated 4H-SiC (0001) substrates cut 8° off-axis toward 〈1120〉. Hydrogen peroxide (H2O2) and potassium nitrate (KNO3) were used as the electrolytes while using colloidal silica slurry as the polishing medium for removal of the oxide. The current density during the polishing was varied from 10 µA/cm2 to over 20 mA/cm2. Even though a high polishing rate can be achieved using high current density, the oxidation rate and the oxide removal rate need to be properly balanced to get a smooth surface after polishing. A two-step ECMP process was developed, which allows us to separately control the anodic oxidation and removal of formed oxide. The optimum surface can be achieved by properly controlling the anodic oxidation current as well as the polishing rate. At higher current flow (>20 mA/cm2), the final surface was rough, whereas a smoother surface was obtained when the current density was in the vicinity of 1 mA/cm2. The surface morphology of the as-received wafer, fine diamond slurry (0.1 µm) polished wafer, and EMCP polished wafer were studied by high-resolution atomic force microscopy (AFM).

Application of Raman microscopy to the analysis of silicon carbide monofilaments.

Abstract: This paper reviews recent research upon the application of Raman microscopy to the characterisation of silicon carbide monofilaments produced by CVD (chemical vapour deposition). It is demonstrated that Raman microscopy is an invaluable technique allowing qualitative information about stoichoimetry variation in silicon carbide monofilaments to be obtained, as it readily detects both crystalline and amorphous carbon and silicon. It is shown that it is possible to characterise the morphology of the SiC crystallites in the monofilaments from analysis of the Raman line shapes. It is also demonstrated that Raman spectroscopy can be used to follow deformation of SiC monofilaments and to determine residual stresses in SiC-monofilament-reinforced metal-matrix composites. In addition, it is shown that it is possible to evaluate internal stresses in the carbon coatings of SiC monofilaments.

Minimum ionizing and alpha particles detectors based on epitaxial semiconductor silicon carbide

Abstract: The relatively high value of the energy required to produce an electron-hole pair in silicon carbide, SiC, by a minimum ionizing particle (MIP) against the value for Si, imposes severe constrains in the crystallographic quality, the thickness and the doping concentration of the SiC epitaxial layer used as the detection medium. In this work, a 40 /spl mu/m thick 4 H-SiC epitaxial layer with a low doping concentration of /spl sim/5/spl times/10/sup 13/ cm/sup -3/ was used in order to have a relatively high number (/spl sim/2200) of e-h pairs generated by a MIP and to deplete the total active layer at relatively low reverse bias (60 V). The detectors are realized by the formation of a nickel silicide (Ni/sub 2/Si) on the silicon surface of the epitaxial layer (Schottky contact) and of the ohmic contact on the backside of a 4 H-SiC heavily doped substrate. We present experimental data on the charge collection properties with /spl alpha/-particles from /sup 241/Am and /spl beta/-particles from /sup 90/Sr. In both cases, a 100% charge collection efficiency, CCE, is demonstrated and the diffusion contribution of the minority charge carriers to CCE is pointed out. The charge spectrum for MIPs from /sup 90/Sr shows a full detection efficiency with the pedestal (noise) clearly separated by the signal (Landau distribution) at reverse bias values comparable and higher than the one needed to totally deplete the layer. Moreover, no degradation was observed at 94/spl deg/C in the CCE and in the energy resolution of the /sup 241/Am alpha-signal from the SiC detector.